When home video cameras came on the market, the sexually adventurous were among the first customers, and since then there's been no shortage of amateurs recording their bedroom antics and often sharing the results.

But not everyone is willing to let their recordings get into the public arena, and the victims of sex tape misadventures include celebrities and everyday people alike.

Sex Tape seems a bit behind the times as ideas for comedy films go, and tries to lift Cameron Diaz out of her slump of bad comedies (Bad Teacher, What To Expect When You're Expecting, The Other Woman) by pairing her with Jason Segel as a suburban couple who lose control of their light-hearted sex video.

But it can't make up its mind whether it wants to gripe about relationship difficulties or throw itself headlong into slapstick farce.

Annie (Diaz) and Jay (Segel) are 30-somethings who fell in lust at university and used to have sex every chance they could get, but their sex life has flatlined since they had kids.

One weekend when the kids are away, they decide to spice things up by videoing themselves doing the wild thing. Wouldn't you know it, Jay accidentally sends the file to people whom he has given tablets as part of his job.

The timing couldn't be worse, with Annie about to land a lucrative commercial deal for her motherhood blog (Really? Another one?), so they set out to retrieve the tablets, while also trying to ensure the file doesn't get into the cloud.

Diaz and Segel's chemistry is adequate at best - they spend a bit of time in the buff (tastefully), but the clumsy, comedy lovemaking isn't anywhere near as funny as that in films like The Tall Guy.

Diaz and Segel would have benefited from snappier comic timing as well - in fact, the film feels like a sitcom episode that's been padded and stretched, and gets downright silly at times, with a bit of violent slapstick and drug- fuelled hyperactivity.

Rob Lowe appears in a supporting role - another example of his self-deprecating response to his own sex tape misadventure - but he's only mildly amusing as a clean-cut tycoon with his own guilty secrets.

There are a few trite speeches to reassure us that Jay and Annie's relationship isn't based on mere lust, and that they really love each other - but overall, Sex Tape is too lacking in vim and daring to work as a farce, and too sloppy and foul- mouthed to work as a rom-com.